Helicopter rotor mounting and drive



April 20, 1948. 2 PU UN v 2,440,225

HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20, 1944 9 Sheets-Sheet 1 AIIORNEYS HELICOPTER ROTOR MOUNTING AND DRIVE April 20, 1948. G, PULUN v 2,440,225

HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20, 1944 9 Sheets-Sheet 3 A Q 2 2% k3 1 m Q v3 S R Q Q m g w a k) 3 April 20, 1948. c, PULLIN I HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20, 1944 April 20, 1948. c. G. PULLIN 2,4

HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20. 1944 9 Sheets-Sheet; 5

April 20, 1948. at. e. PULLIN HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20, 1944 9 Sheets-Sheet 6 April 20, 1948. c, PULUN- 2,440,225

HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20, 1944 9 Sheets-Sheet 7 Z ATI'ORNE VS April 20, 1948. c. G. PULLIN HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20, 1944 9 Sheets-Sheet 8 W m Q/ WMK April 20, 1948. 6. PULLIN 2,440,225

HELICOPTER ROTOR MOUNTING AND DRIVE Filed May 20, 1944 9 Sheets-Sheet 9 w ym vs Patented Apr. 20, 1948 Cyril George Iullin, Wimbledon, London, England Application May 20, 1944, Serial No. 536,547

In Great Britain May 18, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires May 18, 1963 20 Claims. 1

This invention relates to helicopter rotors, rotor mounting and drive, and more particularly to controllable rotor systems, the invention being especially useful in helicopters having a mechanically-driven direct-control sustaining rotor of the tilting-hub type characterized also by torsional flapping, i. e., blade flapping correlated with pitch change (either by an oblique flapping pivot or by a system of pivots and suitable constraints) in such wise that blade pitch angle varies with flapping angle, preferably being uniquely dependent on flapping angle.

In such a torsional flapping rotor considerations 'of stability require that pitch angle decrease with upward .iiapping.

In a rotor of this type angular acceleration of the hub gives rise to a complex system of inertia loads which, besides causing undesirable stresses on the blade roots and pivot pins and uneven loading of the pivot bearings, imposes, because of the flapping and pitch variation, unsymmetrical forces on the hub; these are transmitted, via the axle member, to the controls.

Now, with a tilting hub the drive must be applied through some kind of flexible transmission. If an ordinary cardan joint is employed the angular velocity of the driven member varies periodically with respect to that of the driving member, unless the two members are coaxial, the frequency being twice per revolution and the amplitude increasing with the angle between the axes of the'two members; if the driving member rotates at constant angular velocity to, the angular velocity of the driven member fluctuates twice per revolution through the range cos 0 to w/COS 0 where 6 is the angle between the axes. Such a drive will therefore cause fluctuating stresses on the blades and their pivotal attachments and oscillating loads on the controls, both of frequency twice per revolution, and owing to the high values of the maximum angular acceleration in each oscillation these loads are very heavy.

An object of this invention is to overcome this dimculty with especial reference to the control problem, because the problem of blade and pivot stressing can be met to some extent by increasing factors of safety and by employing drag pivots, allowing lead and lag of the blades, preferably with dampers, but the effect on the controls makes them diiiicult to operate and may result in the aircraft becoming practically uncontrollable.

The present invention attains this object by combining with a tiltable, and more particularly with a controllably tiltable, helicopter rotor, a

. 2 driving transmission employing a constant velocity or homokinetic joint whose centre, that is the point of intersection of the driving and driven axes, is substantially or nearly coincident with that of the universal or gimbal mounting of the rotor axle member.

The constant velocity joint or/and its connections may be so arranged that the rotative members of the joint are not subjected to axial or side ing and driven members are connected by a com- 20 bers, spherically jointed on one another.

known types of constant velocity joint are mepound joint having universal rocking freedom and which possesses some axial freedom, the shafts beinglocated by non-rotary casing mem- Other chanically equivalent, being composed in essence of a pair of shaft locating non-rotary casings universally jointed on one another and a shaft joint- 26 ing component consisting 'of a pair of closely coupled cardan joints combined with an axially slidable joint. 'All such types of joint either possess inherently the axial slidability between the shaft jointing members (e. g. the Tracta 30 joint), or include an axially slidable connection.

The axial slidability substantially prevents axial loads from being transmitted from the driven to the driving shaft; and the duplication of the cardan joint elements combined with the axial slidability substantially prevents the transmission of side loads as well. Such loads are therefore carried by the casing members. In the application of such a joint to this invention the gimbal or universal mounting of the non-rotative rotor axle member itself preferably constitutes the non-rotative casing part of the constant velocity joint and this part of the assembly carries the thrust and side loads of the rotor, the pivots of the gimbal or like mounting being unaffected by the torque load carried by the components of the constant velocity joint proper.

Other types, however, of constant velocity joint are known, the rotative portions of which are not inherently incapable of transmitting axial load; for instance the type having male and female spherical shaft ends connected by balls located in loxodromic intersecting grooves in the spherical members. If this type of joint is used, or an equivalent thereof, a splined joint,having axial freedom, is introduced between the driven 3 member of the joint and the hub member of the rotor. Alternatively, a fully floating driving shaft embodying a splined joint may be used.

It is an object ofthis inventiontoensure that the loads imposedon, the flying controls are, as far as possible, independent of the torque transmitted to the rotor and this object is substantially achieved by the arrangements described.

As the universal suspension of thetiltablqa -Xle '10 member has to carry the thrust and side loading of the rotor, at gimbal suspensionis preferred to any form of spherical joint, because the-pivots of the former, at which the load transmission occurs, can readily be provided withza'mple bean ings of ball or roller type adaptedto carry end as well as radial loading, the provision of. adequate antifriction bearings with a spherical type of joint being a matter of some difiicultyw, Any excessive friction in the universal suspension of the axle'memberwill-adversely afiect the operati011150f the controls.., ,Eurther, the gimbal struc- *t-ure is inherently resistant to torque and provides ion-a simple-solution of design. problems connected with theprovision f arotor brake, the stationary parts of whichlmust be carried by the tiltable hub-member.. If-a spherical joint were used an additional constraint of robust construc- 'tion wouldrhave to bepincorporated to prevent relative rotationiof the-joint-members about. the

axis. of rotation; of .the rotor under the braking torque; and-the. detail design of such constraint wouldpresent problems of some difficulty. t-Howithe foregoing-obiectsare attained, and

, others; whichawill hereinafter appear, will be .un- I derstood from -the following. description with ref-- erence to the actom zaanzrving drawings ,of. a preferred embodiment, of-the invention the scope of which isdefined in the appended claims.

' In the drawings:r---. r-

- Figure-1- is ,a; somewhat diagrammatic in side elevation,partly-in section, of a helicopter embodying I theainvention; Y

. Figurezlisa.view in section oftherotor hub and attachments of one;

diagrammatic view of the s ame in 4 tion of the control housing (shown at95in Figure 6);

Figure 9 isya -view-; in section taken along the line 9-9 of-'Fi-gure 8;-, and I v Fig-ures lO and 1 1. are two, views-in elevation, taken at right angles to oneanother, of the parts comprising the. constant velocity joint of the rotor drive. i I

Referring; to Figure 1, the helicopter includes a body 2|, undercarriage elements,2 2,-elevator 23, vertical .fin 24 and-rudder 25., Within the body is mounted the engine 26,' which drives the rotor through gears contained in gear boxes2l, 29 and a transmission shaft. 28. The.'1 inal drive shaft is containedin, a casing 30 forming an extension of the gearbox 2'9.

. -:The rotor hub is shown at Si land; the lifting rotor blades -at 32.-- I

- Referrimnowrto Figures 2f3, 4 andI SQ the f casing 33 of Figure 1 is extended upwardly by a'hol- 4 low support member 33 terminating in a forked end 34 which supports a gimbal ring 35; this in turn supports a hollow axle member 36. The gimbalring 35 is provided with four equally spaced inwardly, projecting bosses--31 carrying trunnions 38 provided with ball bearings 39. One pair of trunnions articulates with the ends of the supporting fork 34 and the other pair of trunnions with the axle member 36, on which the hub 3| is rotatably mounted by means of ball bearings 40,

4 l. I II The rotor inthis-example has three blades, to

support which the hub is provided with three :l inl s 4 i are secured by taper pins 45 to the pins '44. Lead/lag displacements of the rotor blades are accommodated by movement of the drag links and pivot pins relatively to the hub ears 42.

.Secured by taper pins 41in the drag link 43 is aifif r ihg ivot .pin' is and rotatably mounted thereon by means of needle bearings 1491s. afbla'de root-supporting link 50110.11 which thebladeis rotatably mountedffor torsional, i, e., "pitch yaryi'ng displacment' 'byme'a'ns of, a ball thrust bearngsa, a preload bearing 53 and a, preload' nut 54. The mainspa r of the b1adef(32) is shown at Eitijan'd is screwedfinto a blade. 300 hqusing 5| whichissupported'on'the bearings 52', 53,

In order to'obtain the stable torsional/flapping characteristic, the torsionalfand flap'ping" dis- I placementsiofthe, blade are' ,inad'e interdependent by means of a; linkage comprising alever 58 secured'to the blade and an armffil, 152 lying approximately parallel ,to"the blade and on the leading sidev thereof, and ,js'ecured' to the flapping pivo't pin' This construction is 'shownin Figures 3, 4. and 5 V pairof idgft sesame the spares carries. pivot studs 51' onwh'ich thelever 58, which is forked, articulates. IfIhe forward end "of this lever carries studs, 59,with sphericalseatings I whichengage aball fifl formed on the'end of the arm part Bl ;.the1other end of the latter is tapered toffit a taperlsocket of afbioss163 formed on the tegral' withlthe'fiappi'ng pivdtlpin', 48.

Since he; p njaa 116 kedto" the; me link,

the. arm s 1'," 62K is prevntedi from flapping fWith ',,e e"s1aae,., withthe resuItQt'hat when the blade blade spar' to rotate about'thebladersupport- ,in'g' link; 521 i 0' the bearings? 52.,"531 in thej'direction .fo'rld'ec aslrigfthelpitch', angle of Ithe'blade.

I Conversely, downward flapping is accompanied imitation IQ u 'warrana downward flapping is, provided by means of a' vstop plate 68;. formed integrally with the drag link as and having upperand lower faces 69, '10 which engage'the inner surface it of the blade-supporting" link control mechanism. of the tilting hub, the pilots I seat is indicated at 12. I In the conventional position is acontrol'column 'i 3, pivo ted at 14 to a crank 15' integral with a rockingshaft la supported in abearing l'"l and carryin'g a sprocket 18. The control column. is also pivoted at 19 to V a-pushrpull rodiseactuating 'a'cr'ank Si'carryinga 'sprocke't 82;

A chain or cable 83"is' passed over the' sprocket 18 and over another sprocket 84 which is fast on a further sprocket 85. I

Similarly a chain or cable 88 connects the sprocket 82 with a sprocket 89 fast on yet another sprocket 90. Sprockets 8 4, 85, 89, 90 are coaxial as shown in Figure 6, but for convenience in following the run of the controls the pairs of sprockets 84, 85 and 89, 90 respectively are shown in Figures 7 with their axes separated.

Sprocket 85 carries a chain or cable 86 which is also passed over a sprocket 81 within a control housing 95, while another sprocket 92 within this housing (see Figure 8) is actuated by a chain or cable 9| which is passed over sprocket 98.

The chains or cables 86, 9| are also passed over four jockey pulleys 93, (indicated diagrammatically in Figure 7 by a bar 93m).

Referring now to Figures 8 and 9, the control housing 95 is secured to the upper end of the casing 30 enclosing the final rotor drive shaft (see also Figure 6). The sprocket 92 is mounted in this housing on bearings 96 and is integral with'a sleeve 91 having a quick pitch female thread 98 formed therein. This thread engages a corresponding male thread 99 formed on a bar I on which a sleeve portion IIlIaintegral with a link member I 0| is rotatably but not slidably mounted by means of bearings I02. The sleeve portion I9Ia is slidably mounted in the housing 95 by means of bushes 95a.

The link member also carries a divided pivot pin I01, secured by means of a through-bolt I08 and nut I09, and having rotatably mounted thereon, by means of bearings H0, a forked link III whose other end carries a spherical race II2 enclosing two cages of balls I I3 running on races II4 carried by a cross-shaft H5 which is free to slide endways and to rotate. One end of shaft H5 has splines H6 engaging corresponding splines of the sprocket 81, which is rotatably mounted in the housing 95 by means of bearings H1. The other end of shaft H5 has a male quick pitch thread H8 engaging a corresponding female thread H9 in a sleeve I20 secured in the casing 95.

The link member IOI also has formed thereon a spigot IIlIb carrying a male spherical element I03 engaging spherical seatings formed in a collar I04 and a nut I05 secured to the socket end I09 of a lever 94 which is integral with the rotor axle member 36 (see Figures 2 and 6). (It will be remembered that the axle member 36 is supported on the gimbal mounting 34, 35 and has the hub 3| rotatably mounted on it).

Fore and aft movement of the control column causes the sprocket 92 to rotate by means of the operation of the intermediate elements 80, 8|, 82, 88, 89, 99, 9|, and the thread elements 98, 99 cause the bar I00 to move axially carrying with it the link member IIlI, IIIIa, IIlIb, which thereby actuates the lever 94, I06 to tilt the axle member 36 and with it the hub 3| in the fore and aft plane.

Similarly, transverse movement of the control column acting through the intermediate elements 15, 16, 18, 83, 84, 85, 86 rotates the sprocket 81 and shaft H5, which is caused by the thread elements H8, H9 also to slide endways and this moves the forked link III to rock the link member I9I, IOIa, I9Ib transversely on its bearings I02 and this in turn actuates the lever 94, I06 to tilt the axle member 36 and with it the hub 3| in the transverse plane.

The rotor hub 3| is driven by means of a constant velocity or homokinetlc joint of the 6 loxodromic type illustrated in Figures 2, 3,10 and 11.

The final drive shaft-is shown at I 2| and is supported in the supporting member 33 by means of a bearing I22. Its upper end has a pair of integrally formed jaws I23 and an integral central spigot I25. The interior faces of the jaws have formed therein loxodromic grooves I24.

The driven member of the joint consists of a shaft I21 having integrally formed therewith a pair of jaws I28, having internal loxodromic grooves I29, and a central spigot I30, the whole corresponding to the driving member of the joint.

The joint is centralised by means of a central ball I32 engaging spherical seatings I26, I3I formed in the ends of the spigots I25, I30 and the drive is transmitted by four balls|33 engaged in the loxodromic grooves of the jaws I23, I28, each'ball engaging one groove of a driving jaw and one groove of a driven jaw. Each of the four jaws (two driving and two driven) thus has two grooves, inclined at equal and opposite angles to the transverse circumferential line of the joint.

The driven shaft I21 is Provided with splines I34 engaging corresponding splines in a driving plate I35 which drives the hub 3| through a freewheel coupling I36 loaded by a spring I31 retained by a cap nut I38.

The splined joint I34 prevents any axial loads from being transmitted by the constant velocity joint, which is concentric with the gimbal mounting of the axle member 36. All side loads imparted to the hub or the axle member by control reactions or forces acting on the rotor blades are transmitted by the gimbal mounting to the supporting member 33, 34 and the constant ve-' locity joint is therefore subjected solely to the driving torque.

The rotor blade mounting, blade pitch regulating mechanism, and other features are claimed in my copending application 536,548, filed May 20, 1944. 1

What I claim is:

1. In a helicopter, an airframe, a sustaining rotor having blades independently pivoted to a hub for flapping in planes containing the blade axis and the rotational axis and in such a way that the blade pitch angle varies with and is uniquely dependent on the flapping angle, the pitch angle decreasing with upward flapp said hub including a non-'rotative hollow axle member, universal joint means connecting said axle member to the airframe, a pilots control, means connecting said pilots control and the axle memher for controlling the magnitude and direction of the inclination of the latter from its neutral position, a prime mover and transmission means connecting the latter to the rotor for driving the same and including a homokinetic joint within, and whose centre is substantially coincident with that of .the universal mounting of, the rotor axle member. I

2. In a helicopter, an airframe, a sustaining rotor having blades independently pivoted to a hub for flapping in planes containing the blade axis and th rotational axis and in such a way that the blade pitch angle varies with and is uniquely dependent on the flapping angle, the pitch angle decreasing with upward flapping, said hub including a non-rotative axle member, universal joint means connecting said axle member 1 to the airframe, a pilots control, means connecting said pilots control and the axle memand-22a.

bier for; controlling. the .magnitu =andadire t on' of the inclination of the latter from its neutral: p si s a: prime. mover; and-transmission mean connecting; the; latter. tosthe :rotorqfor:drivin vtha same; and including: ar-homokinetic; joint said. transmissionmeansalsormcluding;anax a 'yfi idv' ablezjoint locatedibetweengthre driven member of: the .homokinetic jointiand thezrotor hub:

3 In ajcontrollableiaircraft'rotor system-m m: prising-iblade means adaptedaato berotated; about; art-taxis;- meanszefiective upon .the blade ;;means for: controllably. alteringztheirmlane ,of trotation; for; shifting their thrustiline; a non-erotatiyelsupe. port about which the blade means rotate,.,,and power-transmitting. means f or driving said blade means including;a;homokineticrangling;joint centered; within said support and; accommodating said alteration of;plane.ofrotations.

4i A construction; accordingatoclaimz 3 wher n saidvhomokineticlsj'cintjs 10f 1thegloxodromic type 51'. The: construction: of: claim: 33' wherein said rotor has alhubi rotatable :on'ssaidtnonerotatable support and:said;joint isthus housedcwithimsaid support and hub;.

6. A construction according to claim .3- where in pivotal: mounting; mechanismjs mrovldedL'for the blade means;;said-:mechanismiprovidi :a virtual 'ipoint sqrs axis of pivotation; centered; at, the center of said joint '7. A construction according tomclaimz firwheree. in therehls aihubluwhich is. mountedgtoggmoveton saidivirtualpointor-ax-is. .of;- pivotation; andawhere in:said pivotimechanism. imaddition .tozsaidr virtual point orraxisstof pivotatiQn;;provides-.also one cr -more axesv of. plvotatiom:ofiilthezblade means with reference .tothe hubs.

8. A constructionraccording totzclaimfl I wherein satpluralitytof: rotor blades comprisathe blade means referred; toand: wherein: eachl-of-said blades is independently pivoted on the hubz-for-mhve ment at least inthe pitchvaryingisenses.

9.4 an; aircraft sustaining; rotor system com-e prising-blade -means adapted; .to be rotated about a generally upright axis, mechanism providing for universal motion of the blade meanswithrreferenceetoa point rontthei. generally; upright) axis, means effective upon: ltheisbladel-means for "con trolla-bly. .2 altering; the; plane of rotation tor said blade zmeans for shifting their; thrust line; a: non-- rotative r support: about: which: the: blade; 1 means rotate; :and powertransmitting. means: for driving said bladevmeans. including :a homokineticangling jcintrenteredwithin said-support and acc mw datingsaidalteration-of:plane. .Ofrotations l0.-t;.' .'he5;c0nstructi0n ,ofizclaim .9" Wheheln"t1il8 centerzofisaid; j cint is: adjacent the :center f uni:- velfsalxmotion of the blade means;

11.1 Thelconstruction of:claim:l0awherein=there istag-rqtative :rotor hubmounted on .saidl-nQnu-rotative-nsu ncrtpand wher n: he m a sm 11 vidingion-{universal motion of I the blademeans comprises; -,=.a:-luniversallmounting? for same-non,- rotativ rsup or v- Y 12. An aircraft sustaining rotor comprising bladameans adapted to :be rotatediabout an approximamly upright -.axis,-:- a rotatablewmember carrying; said blade =means la-mountingr provided for r tilting; of; 'said memberz and adapted-- to take rctior lift 1 thrust;- and ypowertransmitting means adapted .to @drive' s id; blade. means including a homokinetic-rjoint disposed concentrically within missionzmcchanism includingacentrally;disposedtorquerztransmitting;ihomokinetic joint; substantiallyafreeg-ofj Ithe::rotor--1i-ft thrust, anda rotor tilting mounting;througlrwhich the rotor lift thrust islcarried; disposed circumferentially cf said-joint and:.providing; for. tilting; the-:plane ofnrotor-rotationjwith? reference to .lt'he center ofsaidzj ointi 1411A.- cons'truction according-toclaim-13 wherein "saidzmounting. .includesra. gimbal ring assembly dispoosedo peripherally. of ;the--.:central:itransverse planesoi ."said .J' Qint; a. nonerotative axle -.member universally tiltable onsaidz'gimbalr 'ring'zassembly, andlzaarotor lhub rcarrying the blade means :and having bearingsybetweemit and said axle member;

15b A constructionaccording ;to:.c1aim 14 where-.- incthe rblade meansromprlse a. plurality-.ofnblades having-individual. pitchpivot mountings.- on: said hubs.

16;)mconstructionaccording 13056121311 14 where'- in the blade meansa.comprlseiaplurality :of' blades havingzzindivicluala :universa't mountings. on said hub.

17. In: aircraft :sustaining irotor 'rconstructi'on, comprising :blade means. adapted tocbe rotated about an approximatelyuprightcaxis,rotor trans.- missionimechanismiincludingrarcentrally disposed torqueetransmitting; homokinet-ic joint; substantiallyuree of the r-otor liftthrustpan';overrunning drivie @connection in series with: said' homokinetlc jdinacandiaafiotortilting mounting; ,throughwhich thecrotor :liftxthrust. is..carried;: disposed-r circumferent-i'ally 10? said joint: and; providing for: tilting the iplaneloft rotorrotatiom with reference to: the centercofisaid'joinim 18-; .The :constru'ctidmofl claim- 17: wherein said overrunning idrive connection is operativelyiinterposed-l between-said homokinetic'j oint, and the rotorlsblade means; whereby-:the rotor blade 1 means may overrumthe power transmission through-said joint.

19;;A; construction-- according v toclaim 18, whenein the-lovernunning drive connection includes a springiipressed member having an-axially slidable'zd-riveconnection with a member of said joint whereby; said-j ointis relieved of. axial load whether or not/ the notoris overrunning .the. drive.

20, A construction-Iaccordinglto claim-3,- WhereinlythdTOfiOI'fiCQmpITiSESw a hub and a plurality .of blades which are-pivotedto-the hubfor. swinging inta; IdirectiOn, generally transverse the planeof rotation of; theroton and wherein-the blade pitch is;alteredwi-th-suchswin ing:

CYRIL'A GEORGE PULLIN.

REEERENCES TCITEDTI The following reie'renees are ofirecondginyithe file .zofi'lt-hisi patent;

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2;16.3-,8 93.: Scha-irer June 27,1939 22531568.:5 Campbell: Nov..25;-1941 2352;404 Pit-cairnnna June 27., 1944 21356592? Platti, Aug-.;22,-1944 

